JP2007104779A - Method for current offset adjustment and power conversion equipment using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power converter wherein a current detection offset can be accurately adjusted. <P>SOLUTION: A PWM converter includes: a power supply 1; a voltage phase detector 5 that detects the voltage phase of the power supply; semiconductor switches 3 that are connected to the power supply and can be independently turned on and off; a capacitor 4 that smoothes a voltage rectified by the semiconductor switches; and current detectors 6 that detect currents passed through the semiconductor switches. Adjustment of offset in the outputs of the current detectors is carried out by detecting a period A for which a current is not passed based on the phase information of the voltage phase detector. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to offset adjustment of a current detector that detects an input current in a PWM converter.

As for conventional current offset adjustment, in an inverter, a method of performing offset adjustment of a current detector in a base block state where a motor is not driven is generally used.
FIG. 3 is a block diagram of inverter driving showing a conventional current offset adjusting method. In the configuration of the inverter as shown in FIG. 3, the current detector 6 is disposed between the switch group 32 and the load motor 10. Accordingly, the detected value of the current detector 6 is transmitted from the DC bus of the inverter through the power supply circuit 8 during a period in which no current flows (for example, a period in which the inverter is not operated and will be referred to as a base block period in the future). It is possible to make corrections by taking in the controller 11 which operates by inputting power and reflecting the deviation from zero as an offset value in the switch drive circuit 13.

As a method for performing offset adjustment for current detection during motor operation, the motor output current is separated into a torque component (q-axis) and an excitation component (d-axis), and the d-axis component and the voltage phase calculated inside the control controller are used. The offset amount is estimated from the command (see, for example, Patent Document 1).
As described above, the conventional offset adjustment method of the current detector uses a method of performing offset adjustment when the inverter is not driven or estimating from the current detection result and the command value inside the controller.
International Publication No. 00/14866 (page 27, Fig. 1)

However, among the conventional current detector offset adjustment methods, the method of adjusting the offset of the current detector when the motor is not driven in the base block state is the simplest and most effective means in an inverter. It cannot be applied to offset adjustment of the input current detection circuit of the PWM converter that is always connected. In other words, even if the PWM converter is not in operation, there is a problem that this method cannot be applied because a slight current flows when the power source of the control controller is created from the DC bus.
Moreover, although the method of Patent Document 1 can be applied to a PWM converter, there is a problem that an estimation error occurs because it is estimated from a voltage phase command calculated inside the controller.
The present invention has been made in view of such problems, and a current offset adjustment method capable of accurately adjusting the offset of a current detector even in a PWM converter that is always connected to a power supply and a method for using the same. An object of the present invention is to provide a power conversion apparatus.

In order to solve the above problem, the invention described in claim 1 is a voltage phase detector that detects a voltage phase of a power supply, a semiconductor switch that is connected to the power supply and can be turned on and off independently, and is rectified by the semiconductor switch. In a PWM (Pulse Width Modulation) converter comprising a capacitor for smoothing the voltage and a current detector for detecting the current flowing through the semiconductor switch, the voltage phase detector adjusts the offset of the output of the current detector. The period A during which no current flows is detected by detecting the input phase θin, and the offset adjustment is performed in the period A.
According to a second aspect of the present invention, a voltage phase detector for detecting a voltage phase of a power supply, a semiconductor switch connected to the power supply and capable of being turned on and off independently, and a voltage rectified by the semiconductor switch are smoothed In a PWM (pulse width modulation system) converter comprising a capacitor and a current detector for detecting a current flowing through the semiconductor switch, a voltage phase detector for detecting a period A in which no current flows by detecting an input phase θin; And a controller for performing current offset adjustment in the period A detected by the voltage phase detector.

  According to the present invention, in the PWM converter that is always connected to the power supply, the period A in which no current flows can be detected based on the phase information of the power supply voltage. Therefore, the current is detected accurately by performing the offset adjustment in the period A. It is possible to adjust the offset of the instrument.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an offset adjustment method for a current detector according to the present invention.
In the figure, a three-phase AC power source 1 is converted from an AC voltage to a DC voltage by a switch group 3 (comprising semiconductor switches Spr to Snt and flywheel diodes Dpr to Dnt) of a power converter (in this case, a converter). Smoothed by the electrolytic capacitor 4. In this example, the semiconductor switches Spr to Snt use IGBTs (insulated gate type bipolar transistors). However, any switches can be used as long as they can be turned on and off independently.
Between the three-phase AC power source 1 and the switch group 3, the switching noise of the switch group 3 is caused to flow out to the power source 1, and is caused by ON / OFF of the semiconductor switches Spr to Snt constituting the switch group 3. An input filter 2 is inserted to suppress the collapse of the power supply when the power supply line is short-circuited.
The controller 11 is smoothed by the output θin of the input voltage phase detector 5 that detects the input voltage phase of the power supply 1, the outputs Ir, Is, It of the current detector 6 for detecting the input current, and the electrolytic capacitor 4. The output Vdc of the DC voltage detector 7 that detects the DC bus voltage and the voltage command Vdc_ref between the P and N terminals that are the output of the PWM converter are input. In the controller 11, the switch drive time calculator 12 calculates the switch drive time based on the input information, and the switch drive circuit 13 transmits the switch drive signals Gpr to Gnt to the switch group 3.

Here, the current detector 6 generally converts a current into a voltage using a Hall element, a shunt resistor, or the like, converts it into a digital value using an AD converter or the like, and is calculated by a control controller. In addition, an amplifier circuit such as an operational amplifier is generally used for these detection circuits. A voltage offset may be superimposed on the current detector 6 and the detection circuit, and an offset adjustment is necessary for accurate control.
Considering the case where the PWM converter shown in FIG. 1 performs the same offset adjustment of the current detector as before, even if the PWM converter is in the base block period, it is supplied from the DC bus voltage to the controller 11 by the power supply circuit 8. Electricity is consumed.
FIG. 2 shows line voltages Vrs, Vst, Vtr and input currents Ir, Is, It of the power supply 1 during the base block period of the PWM converter. It can be seen that even when the PWM converter is in the base block period, a pulsed current flows according to the power consumption of the power supply circuit 8. Thus, in the PWM converter, since the input currents Ir, Is, It flow even in the base block period, the offset adjustment as in the conventional example cannot be corrected with high accuracy.
A pulsed current as shown in FIG. 2 flows into the electrolytic capacitor 4 via the flywheel diodes Dpr to Dnt of the switch group 3 when the three-phase AC power supply voltage is higher than the DC bus voltage. In the present invention, the input voltage phase detector 5 detects the input voltage phase θin, detects the period A in which no current flows as shown in FIG. 2, and the offset adjustment for current detection is performed in the period A.

  In this way, even in a PWM converter that is always connected to a power supply, a period during which no current flows can be detected, so that current detection offset adjustment can be performed with high accuracy.

Although the present embodiment has been described with respect to a PWM converter, it can be easily deployed in a device that detects an input current with a power conversion device that converts an alternating voltage into a direct current (for example, a 120-degree conduction type converter).
In addition, although the present embodiment describes the case of a three-phase AC power supply, it is a technique that can be easily deployed to a single-phase input type power converter.

It is a block diagram of the PWM converter which performs the current offset adjustment of this invention. It is a timing chart which shows the offset adjustment method of the current detector of this invention. It is a block diagram of the conventional offset adjustment method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Three-phase alternating current power supply 2 Input filter 3 Switch group 31 Input side diode bridge 32 Output side switch group 4 Electrolytic capacitor 5 Voltage phase detector 6 Current detector 7 DC voltage detector 8 Power supply circuit 10 Load motor 11 Controller 12 Switch drive Time calculator 13 Switch drive circuit

Claims (2)

A voltage phase detector that detects the voltage phase of the power supply, a semiconductor switch that is connected to the power supply and can be turned on and off independently, a capacitor that smoothes the voltage rectified by the semiconductor switch, and a current that flows through the semiconductor switch In a PWM (Pulse Width Modulation) converter with a current detector that
The offset adjustment of the output of the current detector is performed by detecting a period A during which no current flows by detecting the input phase θin of the voltage phase detector, and performing the offset adjustment in the period A Method. A voltage phase detector that detects the voltage phase of the power supply, a semiconductor switch that is connected to the power supply and can be turned on and off independently, a capacitor that smoothes the voltage rectified by the semiconductor switch, and a current that flows through the semiconductor switch In a PWM (Pulse Width Modulation) converter with a current detector that
A voltage phase detector that detects a period A in which no current flows by detecting an input phase θin, and a controller that performs current offset adjustment in the period A detected by the voltage phase detector. Power conversion device.

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